Usb interface: The usb interface is used for power supply. When using, you can plug this product into a usb interface with an output voltage of 5V, for example: the car comes with a usb interface (5V), and a car charger interface (5V).Specifications: Multi-function buttons: 1. Adjust the FM frequency. After the product is powered on, and before Bluetooth is paired, click the button to change the FM frequency (a total of 87.5MHZ, 95.0MHZ, 103MHZ three frequencies can be selected) 2. When playing a song, click the button to pause and play. 3. Answer the call: When someone else calls in, you can click the button to answer the call.Instructions: 1. Plug the FM01 into the usb interface of the car whose output voltage is 5V. 2. Set the FM frequency band by clicking the button, then turn on the car's radio, and adjust the FM frequency band of the radio to the same as FM01. 3. FM01 has an FM frequency automatic memory function, and each time it is powered on, it will default to the FM frequency when it was used last time.4. After the FM frequency band is set, find the Bluetooth pairing name: FM01 in the Bluetooth settings of the mobile phone, and click to pair. Then the mobile phone will play the music on the speaker of the car. 5. Adjust the volume: when you are playing music, you can adjust the phone's music volume to the maximum, The car volume is adjusted to moderate.It is not recommended to increase the car volume too much, because the louder the car volume, the more serious the noise and distortion will be. Description:This product is mainly used in in-vehicle scenarios, using the latest Bluetooth 5.1 technology and mature FM frequency modulation technology to allow car fans to easily enjoy in-vehicle wireless music.ParameterProduct name: usb bluetooth FM mitterProduct model: FM01Bluetooth version: V5.1Working voltage: 5VEffective probability: within 10 metersAudio output: FM mitter